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https://issues.apache.org/jira/browse/HDFS-13451?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16442046#comment-16442046
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lujie commented on HDFS-13451:
------------------------------
Hi [~daryn]:
I strongly agree that removing the blindly is bad for postmodern debug.
I attach the new patch in which i try to replace NPE with other exception
which can give the real reason. For UGI and offline imag related NPE, I do
not find suitable exception and they remains the same. And could you please
review the new change in the new patch.
> Fix Some Potential NPE
> ----------------------
>
> Key: HDFS-13451
> URL: https://issues.apache.org/jira/browse/HDFS-13451
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 3.0.0-beta1
> Reporter: lujie
> Priority: Major
> Attachments: HDFS-13451_1.patch, HDFS-13451_2.patch
>
>
> We have developed a static analysis tool
> [NPEDetector|https://github.com/lujiefsi/NPEDetector] to find some potential
> NPE. Our analysis shows that some callees may return null in corner case(e.g.
> node crash , IO exception), some of their callers have _!=null_ check but
> some do not have. In this issue we post a patch which can add !=null based
> on existed !=null check. For example:
> callee BlockInfo#getDatanode may return null:
> {code:java}
> public DatanodeDescriptor getDatanode(int index) {
> DatanodeStorageInfo storage = getStorageInfo(index);
> return storage == null ? null : storage.getDatanodeDescriptor();
> }
> {code}
> it has 4 callers, 3 of them have !=null checker, like in
> CacheReplicationMonitor#addNewPendingCached:
> {code:java}
> DatanodeDescriptor datanode = blockInfo.getDatanode(i);
> if (datanode == null) {
> continue;
> }
> {code}
> but in caller NamenodeFsck#blockIdCK have no !null checker, we add checker
> just like CacheReplicationMonitor#addNewPendingCached
> {code:java}
> DatanodeDescriptor dn = blockInfo.getDatanode(idx);
> if (dn == null) {
> continue;
> }
> {code}
> But due to we are not very familiar with HDFS, hope some expert can review
> it.
> Thanks!!!!
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